The present invention relates to an integral foam body and a method of manufacturing the same.
The term "integral foam body" is understood to mean a foam material body of synthetic plastic with an outer skin which is substantially not foamed and normally has a thickness of 0.2 mm-2 mm, as a rule approximately 1 mm. Such an integral foam body has an outer surface whose appearance corresponds to the appearance of a massive body of the respective synthetic plastic but with a substantially lower weight, has a bending resistance which corresponds to the bending resistance of a massive synthetic plastic body of the same dimension but considerably exceeds the weight of the latter.
Integral foam bodies can be produced of duroplastic or thermoplastic synthetic plastic material, whereas the not foamed pore-free outer skin is produced by a suitable tempering of the outer surface of the foamed synthetic plastic.
Methods of manufacturing extruded integral foam shaped members of thermoplastic material are known from DE-OS No. 1,729,076 and DE-0S No. 1,913,921. From DE-OS No. 3,011,692 it is also known to place relatively thick and long staple fibers between the balls of a body assembled from polyvinyl chloride foam balls, and before this they are coated with an adhesive agent. The purpose of this feature is to form a spatial supporting grate for individual foam balls of the polyvinyl chloride foam so as to prevent substantially the cracking of a finished foam body.
It is further known from the DE-OS No. 3,016,333 to mix liquid initial material for duroplastic synthetic plastic to approximately one-third of its weight with very short staple fibers and then mix this mixture homogenously with a gas. The bubbles of the gas in the initial material must replace the gas bubbles produced by a propellant and fixed by the fine staple fibers until the end of hardening of the synthetic plastic. It is also known to embed short staple fibers in extruded, flexible foam of massive synthetic plastic.
Finally, an integral foam body is disclosed in the DE-OS No. 2,745,373, in which staple fibers are added to the initial product used for foaming of an integral foam body of polyurethane in a mold to improve the mechanical properties of the finished integral foam body. The staple fibers are embedded in the integral foam body in statistically distributed orientation. The manufacture of such an integral foam body is expensive, since for each body the mold must be filled, closed and after hardening of the foam body again opened, whereupon the foam body can be removed.